Add VS2013 Support

I modified the extension to build and install on VS2013, and to support the new HTML editor (`htmlx` content type).

I'm not sure how these changes affect the ability to build on VS2010 or 2012; 5a314d422a66847b58dc6a4634e76d21e3a6959f may cause problems.

I also fixed some compiler warnings and improved versioning for references & start action.